Hydrazinium nitroformate propellant with saturated polymeric hydrocarbon binder

ABSTRACT

A solid propellant composition containing hydrazinium nitroformate as an oxidizer, utilizing a saturated polymeric hydrocarbon binder and a polyisocyanate as a curing agent to prevent deterioration of the propellant.

United States Patent Low et 211.

Jan. 2, 1973 Appl. No.: 74,862

US. Cl ..l49/19, 149/36 llnt. Cl. ..C06d 5/06 Field of Search ..l49/19,20, 36, 44

References Cited UNITED STATES PATENTS 3,418,183 12/1968 Rice ..149/36 X3,586,552 6/1971 Potts et al 3,511,725 5/1970 Stevens et al 3,535,17310/1970 Spenadel et a1. ..l49/36 X Primary Examiner-Benjamin R. PadgettAttorney-Monte F. Mott, J. H. Warden and John R. Manning [57] ABSTRACT Asolid propellant composition containing hydrazinium nitroformate as anoxidizer, utilizing a saturated polymeric hydrocarbon binder and apolyisocyanate as a curing agent to prevent deterioration of thepropellant.

8 Claims, No Drawings HYDRAZINIUM NITROFORMATE PROPELLANT WITH SATURATEDPOLYMERIC HYDROCARBON BINDER ORIGIN OF THE INVENTION Aeronautics andSpace Act of 1958, Public Law 83-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention isin the field of solid propellants, more particularly the inventionrelates to solid propellants which contain hydrazinium nitroformatewhich are stable and have a satisfactory shelf life.

2. Description of the Prior Art Hydrazinium nitroformate, HNF, is avaluable oxidizer in that it is very energetic, producing highperformance in the propellants in which it is incorporated. When HNF isutilized with conventional unsaturated hydrocarbon binders, such ascarboxyl terminated polybutadiene, the propellant will deteriorate onaging at ambient temperatures. It appears that the HNF attacks thedouble bonds in the unsaturated hydrocarbon binder, producing agas-forming reaction. The propellants thus become porous and losestructural strength. Not only is there porosity due to the gasformation, but further, the attack of the double bonds breaks down thebackbone of the binder, softening and weakening the propellant. Onemethod for overcoming the deterioration of the propellants containingHNF and unsaturated hydrocarbon binders, is to utilize nitroguanidine asan additive to the propellant mixture. As disclosed in copendingapplication Ser. No. 74,861, now US. Pat. No. 3,658,608 filedconcurrently herewith, to the same inventor, there is described addingnitroguanidine to solid propellant formulations comprised of carboxylterminated polybutadiene and HNF. Further, the invention is particularlydirected to utilizing triethylene melamine as a type of curing agent,since it has been found that some curing agents are also attacked by HNFin addition to the propellant binder. Thus, as disclosed in theaforementioned copending application, one system has been developed topractically allow the utilization of HNF as an oxidizer in solidpropellants. This system, however, is limited to carboxyl terminatedpolybutadiene, or as also indicated in the disclosure, polyisoprene.Further, the invention as disclosed in the copending application, isparticularly limited to curing agents that do not react with HNF yetwill cure the unsaturated type of binders. Since it is desirable toutilize HNF as an oxidizer, it is further desirable to enlarge the typeof solid propellant systems in which this material can be used so thatone would not be limited solely to the system disclosed in the copendingapplication.

SUMMARY OF THE INVENTION The herein invention is directed to a novelpropellant composition comprised of a saturated polymeric hydrocarbonbinder, particularly of a hydroxyl terminated specie, such as hydroxylterminated hydrogenated polybutadiene. It has been found that HNF can beincorporated as a solid particulate oxidizer in these saturated bindersto produce a propellant having satisfactory shelf life if a propercuring agent is utilized. Specifically, it has been found that if apolyisocyanate type curing agent such as polymethylenepolyphenylisocyanate, PAPI, is utilized the aforegoing results areachieved in a propellant having satisfactory shelf life results.Although other polyisocyanates such as toluene diisocyanate, TDI andhexamethylene diisocyanate HMDI can also be used, PAP] is preferred.

DESCRIPTION OF THE PREFERRED EMBODIMENT As pointed out above, solidpropellant formulations containing HNF in unsaturated hydrocarbonbinders deteriorate on aging due to gas-forming reactions within a fewdays at ambient temperatures. Since it is postulated that this is due tothe attack of HNF upon double bonds in the binder, it has led to thepresent disclosure that HNF could be combined with saturated hydrocarbonbinders. Such saturated binders must have present functional groupswhich are capable of being cross-linked to form the cured network. Thus,the herein invention is particularly directed to binders that containfunctional hydroxyl groupings. Examples of such binders are hydroxylterminated polybutylene, hydrogenated hydroxyl terminated polybutadieneand hydrogenated hydroxyl terminated polyisoprene. Once a saturatedbinder system is chosen for the HNF, the problem of deterioration isstill not overcome, as will be shown below from the results of testsperformed. HNF not only will apparently attack unsaturated bonds in thepolymeric binders, but further can react apparently with various curingagents utilized. Thus, for example, as disclosed in the aforementionedcopending application, a particular curing agent such as triethylenemelamine is preferred to cure the carboxyl terminated polybutadienedisclosed therein, having nitroguanidine as an additive. As pointed out,curing agents such as MAPO which is tris[ l-(2-methyl)- aziridinyl]phosphine oxide when used in that same system would produce a gassingand deterioration due to apparent reaction with the HNF. In the samesense, in the herein invention, the choice of curing agent is importantand, in fact, determines the success of the propellant system inovercoming the shelf life problem.

It has thus been unexpectedly found that the utilization of a particularpolyisocyanate type curing agent, namely, polymethylenepolyphenyliscoyanate, PAPI, will cure the hydroxyl terminated saturatedbinders into a cured propellant system that will have a good shelf lifewhen incorporating HNF as an oxidizer. It is to be pointed out that PAPIis a known curing agent. However, unexpectedly this particularisocyanate has been found to be more effective in preventingdeterioration of the saturated binder, than similar known isocyanatecuring agents such as toluene diisocyanate, TDI, and hexamethylenediisocyanate, HMDI.

In the propellant system of this invention, the saturated binder willgenerally comprise 5 to 25 weight percent of the propellant. The HNFoxidizer will comprise 50 to weight percent. In addition to the oxidizerit is generally required that a fuel be present. Any suitable solidpropellant particulate fuel is usable. Typical example of such fuel isparticulate aluminum. Other examples of metal fuels that are usefulinclude beryllium,

boron and magnesium. The solid particulate fuel will be present in anamount that will vary from 5 to 20 weight percent. Often, the saturatedhydrocarbon binders are waxy in nature and require a plasticizer such asConoco 11-35 which is a hydrocarbon oil to be added to improveprocessing. Other suitable plasticizers, such as Oronite Polybutene No.6, dioctyl azelate and isodecyl pelargonate can be used, as isconventional in the processing of these materials. The plasticizer willgenerally vary from 0 to 20 weight percent of the composition. As theplasticizer is increased in level, it is found that the tensile strengthof the cured compositions tend to decrease. Thus, it is desirable tominimize the amount of plasticizer. This can be achieved by utilizinglower viscosity binders as well as elevating processing temperatures. Inaddition to the foregoing ingredients, burning rate modifiers, coolantsand the like which are used in conventional propellant art, if

compatible with HNF, can be added to the compositions in amounts from 0up to 10 weight percent.

The amount of the PAPI curing agent utilized is related to the amount ofbinder material. Curing transpires between the OH groups on the binderand the NCO groups on the curing agent to form urethane linkages. Thus,the critical ratio is the NCO to OH groups. As a result, sufficient PAPIshould be present to provide a ratio of NCO to OH of from 0.95 to about1.3 in the composition.

In formulating the propellant composition of the invention, theingredients are mixed prior to the final addition of the PAPI curative.It is preferred to mix the propellant at a temperature range of to 30C.The formulated propellant compositions are then cured at a temperaturebetween 20 and 30C for 24 to 48 hours to a point where the cure isobtained. It is believed that the invention will be further understoodfrom the following detailed examples.

EXAMPLE I A series of propellants were formulated utilizing differingpolyisocyanate curing agents selected from a class consisting of PAPIand l-IMDI. To illustrate the relative effect of each of these materialsupon the shelf life of the propellant. The propellants all contained 70weight percent I-INF, 12 weight percent aluminum and 18 weight percentof a binder. The binder was Telagen S, which is a hydrogenated hydroxylterminated polybutadiene made by General Tire & Rubber Co. The bindercontained one part by weight of Conoco 11-35 as a plasticizer to fiveparts of Telagen S. The amount of the various isocyanate curativesvaried, and in the following Table I, the effect of the amount ofcurative is shown, based on the ratio of NCO to OH groups present in thebinder material. The results of the test are thus shown in the belowtable.

TABLE I ACCELERATED AGING OF IMPROVED HNF PROPELLANTS (At 45C) HNF/ 12%A1 18% Binder Binder: Telagen S Conoco H-35 plasticizer NCO/HO TimeSwelling Wt. Loss Curative Equ. Ratio Days Vol. Loss PAP] 0.96 12 0.0.02 PAPI .096 24 0. 0.14 A I 1.04 12 0. 0.02 PAPI 1.04 35 0. 0.12 PAPI1.11 12 0. 0.02 PAPI 1.11 35 O. 0.14 PAPI 1.18 12 0. 0.02 PAPI 1.18 350. 0.14 TDI 1.00 12 8. 0.25 TDI 1.06 12 10. 0.40 TDI 1.15 12 8. 0.44 TDI1.25 12 0. 0.02 TDI 1.25 17 11. 0.23 HMDI 1.09 12 0. 0.02 HMDI 1.09 213. 0.24

with 2 parts hexanetriol added per parts Telagen S in order to improvemechanical properties.

As can be seen from the above table, the use of PAPl peculiarly moreeffectively inhibited the deterioration of the propellant system thandid TDI and HMDI. With TDI and HMDI shelflife was increased by the useof an excess of the curing agent. PAPI is preferred because of longershelf life with a lower NCO/OH ratio. A large excess of curing agenttends to give poor mechanical properties.

EXAMPLE II To illustrate the fact that the system requires a saturatedbinder, a propellant was formulated comprised of 13 weight percent R-45Mwhich is an unsaturated hydroxyl terminated hydrocarbon manufactured bySinclair Petrochemicals, Inc., 3.25 weight percent Conoco 11-35 as aplasticizer, 1.7 weight percent PAPI, 14 weight percent aluminum and 69weight percent HNF. This material swelled at the end of 13 days whenmaintained at a temperature of 45C to indicate that when all the otheringredients in the formulation of the same including the use of PAPI,the presence of unsaturated bonds in the binder will lead to attack bythe I-INF to lower the shelf life and prevent practical utilization ofthe material.

I claim:

1. A solid propellant composition comprising:

hydrazinium nitroformate in an amount sufficient to act as an oxidizer,

a saturated polymeric hydrocarbon binder containing hydroxyl terminalfunctional groups, and a polyisocyanate in an amount sufficient to curesaid binder.

2 The propellant of claim 1 wherein said binder is selected from theclass consisting of hydroxyl terminated polybutylene, hydrogenatedhydroxyl terminated polybutadiene and hydrogenated hydroxyl ter- 5 to 20weight percent of solid particulate metal fuel. minated polyisoprene. 6.The composition of claim 5 wherein said binder is 3. The propellant ofclaim 1 wherein said curing selected from the class consisting ofhydroxyl teragent is polymethylene polyphenylisocyanate. minatedpolybutylene, hydrogenated hydroxyl ter- 4. The propellant of claim 1further comprising: 5 minated polybutadiene and hydrogenated hydroxyltera solid particulate metal fuel. minated polyisoprene. 5. A solidpropellant composition comprising: P P P of claim 5 Whercin 5 to 25weight percent ofa hydroxyl terminated satu- 531d curlng agentPoll/methylene yp y rated polymeric hydrocarbon binder, y 50 to 70weight percent hydrazium nitroformate, 10 propellant Composition 0fClalm 5 further sufficient polyisocyanate curing agent to provide acompnsmgi ratio of NCO to OH groups in said composition of up to weghtPermt ofa plastlclzer- 0.95 to 11.3,

1. A solid propellant composition comprising: hydrazinium nitroformatein an amount sufficient to act as an oxidizer, a saturated polymerichydrocarbon binder containing hydroxyl terminal functional groups, and apolyisocyanate in an amount sufficient to cure said binder. 2 Thepropellant of claim 1 wherein said binder is selected from the classconsisting of hydroxyl terminated polybutylene, hydrogenated hydroxylterminated polybutadiene and hydrogenated hydroxyl terminatedpolyisoprene.
 3. The propellant of claim 1 wherein said curing agent ispolymethylene polyphenylisocyanate.
 4. The propellant of claim 1 furthercomprising: a solid particulate metal fuel.
 5. A solid propellantcomposition comprising: 5 to 25 weight percent of a hydroxyl terminatedsaturated polymeric hydrocarbon binder, 50 to 70 weight percenthydrazium nitroformate, sufficient polyisocyanate curing agent toprovide a ratio of NCO to OH groups in said composition of 0.95 to 1.3,5 to 20 weight percent of solid particulate metal fuel.
 6. Thecomposition of claim 5 wherein said binder is selected from the classconsisting of hydroxyl terminated polybutylene, hydrogenated hydroxylterminated polybutadiene and hydrogenated hydroxyl terminatedpolyisoprene.
 7. The propellant composition of claim 5 wherein saidcuring agent is polymethylene polyphenylisocyanate.
 8. The propellantcomposition of claim 5 further comprising: up to 20 weight percent of aplasticizer.